1. Field of the Invention
The present invention relates to a detection-signal transmitting apparatus that detects changes of an object observed and transmits detected signals representing the changes. More particularly, the invention relates to an apparatus designed to transmit detection signals easily to a site that is remote from the object.
2. Description of the Related Art
In some cases, it is required that changes in various objects observed be detected in order to control various electronic devices and that the signals representing the changes be transmitted to a desired site. More specifically, in a grinding machine and the like, for example, the condition in which a grindstone contacts a work piece should be detected in order to control the position of the grindstone. As well known, when the grindstone contacts the workpiece, ultrasonic waves are generated. If the ultrasonic waves generated at the moment the grindstone contacts the workpiece are detected, the condition in which the grindstone contacts the workpiece can be recognized from the level of the signal of the ultrasonic waves. Hence, various apparatuses for detecting ultrasonic waves and transmitting the signal have been proposed.
For example, Patent Document 1 (noted below) discloses a grinding machine, which is hence known to the public. This machine uses a piezoelectric element, which is attached to a grindstone to detect ultrasonic waves that are generated when the grindstone contacts a workpiece. A first coil is connected in series to the piezoelectric element. A second coil is arranged on the central axis of the first coil and thus opposed thereto. The electromagnetic coupling of the first and second coils can induce, at the second coil, the ultrasonic-wave signal detected by the piezoelectric element.
In the conventional grinding machine described above, however, the first and second coils must be precisely adjusted in position to be arranged on the same axis so that the magnetic coupling between them may be effective. Further, sites where the machine can be installed are limited because of its configuration. That is, the machine has small freedom of use. Moreover, the first and second coils need to have so many turns and so large a size that any signal the second coil generates is at a level high enough to be processed well. Therefore, the conventional grinding machine can hardly be as small as is generally demanded.
Patent Document 1: European Pat. Appln. Publication No. 446849